Evidence of Alfvenic Poynting Flux as the Primary Driver of Auroral Motion During a Geomagnetic Substorm

S. Tian, C. A. Colpitts, J. R. Wygant, C. A. Cattell, C. P. Ferradas, A. B. Igl, B. A. Larsen, G. D. Reeves, E. F. Donovan

Research output: Contribution to journalArticlepeer-review

Abstract

Geomagnetic substorms are major energy transfer events where energy stored in the Earth's magnetotail is released into the ionosphere. Substorm phenomena, including auroral activities, earthward Poynting flux, magnetic field dipolarization, etc, have been extensively studied. However, the complex interplay among them is not fully understood. In a fortuitous event on June 7, 2013, the twin Van Allen Probes (separated by 0.4 h in local time) observed bursts of earthward Alfvenic Poynting flux in the vicinity of the plasma sheet boundary layer (PSBL). The Poynting flux bursts correlate with enhancements of auroral brightness around the footpoints of both spacecraft. This indicates a temporal and spatial correlation between the auroral brightening and Poynting flux bursts, and that the auroral motion is directly linked to the perpendicular expansion of the Alfven wave. These observations suggest that the Alfvenic Poynting flux is a primary driver for the auroral electron acceleration. Around the time of auroral brightening, a dipolarization was seen to propagate more than 4 h in local time during a 20 min period. The azimuthal phase speed of this dipolarization (2 deg/min) is too small to explain the azimuthal motion of the aurora (13.6 deg/min), but the dipolarization could be related to the generation of the Alfvenic Poynting flux through phase mixing at strong density gradients like those in the PSBL.

Original languageEnglish (US)
Article numbere2020JA029019
JournalJournal of Geophysical Research: Space Physics
Volume126
Issue number5
DOIs
StatePublished - Apr 16 2021

Bibliographical note

Funding Information:
The authors thank the Van Allen Probes teams, especially the HOPE and EMFISIS teams, for their support. This work was supported at UMN by the NASA grant 80NSSC19K0306 and by the contract from JHU/APL under NASA prime contract NAS5‐01072.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • Alfven waves
  • Poynting flux
  • auroral physics
  • dipolarization
  • discrete arc

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